Potential Thermoelectric Applications in Diesel Vehicles

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1 Potential hermoelectric Applications in Diesel Vehicles by Douglas Crane B, LLC DEER Conference Newport, RI August 25, 2003

2 Automotive echnology Drivers Requirements for reduced emissions and environmental impact Increasing markets for alternative propulsion systems and energy sources Needs for greater fuel efficiency Marked increase in automotive electronics Continuous need for improved passenger comfort

3 Advantages of E s in Vehicle Applications olid-state imple few or no moving parts Able to provide distributed cooling and heating Compatible with new vehicle types ystems do not produce emissions, are recyclable and exemplify environmental friendliness

4 hermoelectric Fundamentals hermoelectrics are couples of n- and p-type semiconductors generate voltage ( sh sc ) across the junctions generate current as a function of heat flux through couples ideally with low thermal conductivity and high electrical conductivity Q H electric insulating layer sh V oc =α( sh sc ) I p-couple I n-couple h + e - sc electric insulating layer Q C

5 hermoelectric Efficiency B hermoelectric efficiency is based on the material s non-dimensional figure of merit (Z) and the across the device From the late 1950 s until the late 1990 s, the highest Z achieved in practice was ~ 1, with little improvement during that time. With a Z = 1 and a = 100 o C, a device efficiency of ~ 5% can be achieved with current technology.

6 Promising Developments in hermoelectric Materials Quantum well devices (MI) Harman et al. (2002) conservatively estimated that Z=2.0 at 300 K could be achieved with quantum well devices. uperlattice thin-film materials (RI) Venkatasubramanian et al. (2001) demonstration of thin film E s with Z ~ 2.4 at near room temperature. Alternative materials (JPL) Fleurial et al. (2001) filled skutterudites (Ln 4 Pn 12 ) with Z of 1.8 at 650 C Efficiencies would approach the 20-25% range for large temperature differences (> 400 K).

7 Promising Developments in hermoelectric Assembly echniques hermal isolation (B) Bell (2002) predicts at least 50% and up to 120% improvement in performance by thermally isolating each E couple in the direction of the fluid flow. Higher efficiencies and coefficients of performance (COP) are achieved by progressively heating/ cooling operating fluid Used in conjunction with advanced thermoelectric materials could provide efficiencies approaching 50%.

8 Potential of hermoelectric Energy Conversion B 7 Cooling Efficiency 6 tandard Possible in 2-4 years B Coefficient of Performance R134a system Commercially available MI + tandard RI & MI Z Horizontal band represents the COP for a system using R134a.

9 Amerigon Climate Control eat (CC M ) Most successful and highest production volume thermoelectric system in vehicles today Mass production of thermoelectric materials will bring costs down.

10 CC Advantages B Improves passenger comfort by targeting strategic areas for climate control Decreases the use of standard HVAC systems, reducing greenhouse gas emissions created by R134a Improves fuel economy by reducing engine load required to drive HVAC system Vehicle weight can be reduced, translating into improved fuel economy

11 Current and Projected CC Vehicle Platforms Number of Vehicle Platfoms (otal) (E) 2005 (E) Year Available in vehicle platforms made by Lincoln, Lexus, Ford, oyota, and Infiniti Will be standard on the 2004 Cadillac Escalade

12 Motivation for Waste Heat Recovery Up to 65% of fuel chemical energy is lost as waste heat in a typical diesel vehicle another 2-10% is used by the alternator to meet electrical loads Fuel Chemical Energy 100% Cooling ystem Heat Loss 25-30% ( f ~ 120 o C) Engine Alternator 2-10% Exhaust ystem Heat Loss 30-35% ( f > 400 o C) Drivetrain Friction ~5% Propulsion 20-35% If accessory loads can be met via waste heat recovery, more fuel energy could be converted directly to propulsion (an increase of 2-10%) Fuel Chemical Energy 100% Cooling ystem Heat Loss 25-30% ( f ~ 120 o C) Engine Waste Heat Recovery Exhaust ystem Heat Loss 30-35% ( f > 400 o C) Drivetrain Friction ~5% Propulsion 22-45% Electrical Loads

13 Motivations for Waste Heat Recovery (cont.) Up to 10 kw of fuel chemical energy can be saved if a E waste heat recovery system displaces an alternator used to produce 1kW of auxiliary power. Like regenerative braking, waste heat recovery can provide additional energy reserves for a hybrid electric vehicle battery pack

14 E Radiator Cross-ection (drawing not drawn to scale) B cool air flow cool air flow E modules d min hot liquid coolant flow d maj fins (louvered)

15 ystems-level E Waste Heat Recovery from the Automotive Cooling ystem Case 1 Case 2 Case 3 (k W ) P n e t P net (kw ) tim e (s ) ransient net power (P E P fan P pump ) for the U06 drive cycle using RI E s with amb = 300 K and f,max = 395 K. Overall vehicle efficiency was shown to improve by as much as 3.3% for standard driving cycles (does not include B thermal isolation).

16 Previous Work on Automotive Waste Heat Recovery from the Exhaust ystem Embry and udor Utah t. University and University of Missouri (1968) heoretically showed an exhaust waste heat E generator could provide sufficient auxiliary electrical power for a vehicle Menchen et al. eledyne Energy ystems (1990) imulated E muffler for a heavy diesel truck Haidar and Ghojel Monash University Austrailia (2001) Predicted that a 1 kw alternator could be displaced by a E waste heat recovery system based on a low-power diesel engine placed between the exhaust manifold and exhaust tube Hendricks and Lustbader National Renewable Energy Laboratory (2002) P E up to 0.9 kw for light-duty and 5 6 kw for heavy-duty vehicles were predicted using a modified ADVIOR vehicle simulator

17 Waste Heat Generation Challenges B Cooling the cold side in an exhaust system Inconsistent airflow along the underside of the vehicle. Increased complexity of additional coolant loop (i.e. pumps, tubing, and control systems). Extracting heat from hot side in exhaust system Internal fins may create engine backpressure concerns Potential aerodynamic drag increase Integrated thermoelectric radiator may further restrict cooling system airflow Additional heat exchanger along underside of vehicle to extract heat from exhaust may restrict and/or disrupt airflow. Additional weight of thermoelectrics

18 Emissions Reduction Applications 60% to 80% of all vehicle emissions occurs during coldstart Reduce cold-start emissions catalyst light-off ignificant problem in hybrid electric vehicles used in urban driving where engine is turned on and off emperature control of catalytic converter for optimum performance Dual-use device could be designed for waste heat recovery and temperature control Reduce cold-start emissions fuel filter Prevent obstruction of fuel filter by solidified fuel Particularly a problem in diesel vehicles since the solidification temperature of diesel fuel is higher than that of gasoline Particulate trap regeneration Raise temperature of particles to 500 o C in order to burn off device-clogging soot that reduces trap functionality.

19 Conclusions B Using B thermal isolation techniques in conjunction with advanced E materials can provide efficiencies and COPs that will be competitive with or exceed the performance of current power generation and HVAC systems. B is also developing higher power density thermoelectrics, which will further reduce weight and cost. hermoelectric applications in diesel vehicles can provide practical methods to improve fuel economy and reduce engine and HVAC emissions as well as increase user comfort.